1,2-Hydrogen atom transfer of aminyl radicals under photoredox catalysis for the synthesis of α-amino phosphine oxides

Abstract

α-Amino phosphorus compounds are significant structural motifs in natural products, pharmaceuticals and organocatalysis. The construction of such motifs by hydrogen atom transfer (HAT), however, is rare. Herein, we describe a photocatalytic net 1,2-HAT of nitrogen-centered radicals for the formation of C(sp³)–P bonds. This net 1,2-HAT proceeds via deprotonation of N-centered radicals without the requirement of external strong bases, instead being facilitated by the benzoate anion generated during the reaction. This process enables the synthesis of α-amino phosphine oxides bearing various functional groups under mild conditions. The gram-scale synthesis demonstrates the scalability of the net 1,2-HAT rearrangement/radical–radical coupling reaction, which has been used in the preparation of an antitumor agent. Mechanistic investigations, including radical trapping experiments, Stern–Volmer fluorescence quenching experiments, cyclic voltammogram studies, cross-over experiments, KIE studies and DFT calculations support a net 1,2-HAT pathway.